netdev - Re: [MeeGo-Dev][PATCH] Topcliff: Update PCH

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Message-ID: <4C9078D3.50300@grandegger.com>
Date:	Wed, 15 Sep 2010 09:42:11 +0200
From:	Wolfgang Grandegger <wg@...ndegger.com>
To:	Masayuki Ohtake <masa-korg@....okisemi.com>
CC:	Marc Kleine-Budde <mkl@...gutronix.de>,
	andrew.chih.howe.khor@...el.com, qi.wang@...el.com,
	netdev@...r.kernel.org, gregkh@...e.de, yong.y.wang@...el.com,
	socketcan-core@...ts.berlios.de,
	Morinaga <morinaga526@....okisemi.com>, meego-dev@...go.com,
	arjan@...ux.intel.com
Subject: Re: [MeeGo-Dev][PATCH] Topcliff: Update PCH_CAN driver to 2.6.35

On 09/14/2010 02:46 AM, Masayuki Ohtake wrote:
> Hi Marc,
> 
>>>> - implement NAPI
>>> Since Topcliff CAN HW register has only single rx buffer,
>>> I think NAPI is unnecessary.
> 
>> Doesn't matter. Please try to implement it.
> 
> Our CAN driver must pull received data from CAN-HW rx buffer as fast as it can
> so that the received data is not over-written by next received data.
> In case of implemented with NAPI,
> since NAPI has time-lagging after receiving first packet,
> probability of over-written(discarded) buffer is to be high.
> Thus, for our CAN HW, we should NOT implement with NAPI but normal "netif_rx".

True, if you just use one RX-Object. But it just helps a little bit and
it would be much better to use the buffering on RX messages in the CAN
controller hardware, either by using more than one RX object, or
combining RX objects to a FIFO, or whatever your CAN controller supports.

Wolfgang.
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